U.S. patent application number 15/934075 was filed with the patent office on 2018-07-26 for optical transceiver with external laser source.
This patent application is currently assigned to Juniper Networks, Inc.. The applicant listed for this patent is Juniper Networks, Inc.. Invention is credited to Massimiliano SALSI.
Application Number | 20180212699 15/934075 |
Document ID | / |
Family ID | 60119873 |
Filed Date | 2018-07-26 |
United States Patent
Application |
20180212699 |
Kind Code |
A1 |
SALSI; Massimiliano |
July 26, 2018 |
OPTICAL TRANSCEIVER WITH EXTERNAL LASER SOURCE
Abstract
A wavelength division multiplexing (WDM) transceiver module
comprising an optical port and an optical modulator is disclosed
herein. The optical port includes a data transmit and receive
optical fiber connector and a laser source-in optical fiber
connector. The laser source-in optical fiber connector is
configured to couple to a laser source external to the WDM
transceiver module, and provide polarization alignment for a
polarization-maintaining fiber. The optical modulator is configured
to receive a laser output from the external laser source via the
polarization-maintaining fiber and modulate the laser output based
on analog electrical signals generated by a digital signal
processor. The WDM transceiver module may not including an onboard
laser source.
Inventors: |
SALSI; Massimiliano;
(Sunnyvale, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Juniper Networks, Inc. |
Sunnyvale |
CA |
US |
|
|
Assignee: |
Juniper Networks, Inc.
Sunnyvale
CA
|
Family ID: |
60119873 |
Appl. No.: |
15/934075 |
Filed: |
March 23, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15485202 |
Apr 11, 2017 |
9967048 |
|
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15934075 |
|
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62408316 |
Oct 14, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 10/40 20130101;
H04J 14/0202 20130101; H04B 10/503 20130101; G02B 6/4292 20130101;
H04J 14/06 20130101; H04J 14/0221 20130101; H04B 10/07955
20130101 |
International
Class: |
H04J 14/02 20060101
H04J014/02; H04J 14/06 20060101 H04J014/06; H04B 10/079 20130101
H04B010/079; H04B 10/40 20130101 H04B010/40 |
Claims
1. A method, comprising: providing, at an optical port of a
wavelength division multiplexing (WDM) transceiver module,
polarization alignment for a polarization-maintaining fiber;
receiving, at an optical modulator operatively coupled to the
optical port, a laser output from a laser source via the
polarization-maintaining fiber; and modulating, using the optical
modulator, one or more components of the received laser output.
2. The method of claim 1, wherein the WDM transceiver module does
not include an onboard laser source.
3. The method of claim 1, wherein the WDM transceiver module is
configured to be coupleable to a host board or to be capable of
being integrated into the host board.
4. The method of claim 1, further comprising: providing, at the
optical port of the WDM transceiver module, an optical pump-in
optical fiber connector configured to be coupleable to one or more
external optical pumps.
5. The method of claim 1, further comprising: providing, at the
optical port of the WDM transceiver module, an optical pump-in
optical fiber connector configured to be coupleable to one or more
external optical pumps, the optical pump-in optical fiber connector
including a specific-wavelength fiber, an operative wavelength of
the specific-wavelength fiber substantially matching a wavelength
of a laser from the one or more external optical pumps.
6. The method of claim 1, wherein modulating the one or more
components of the received laser output includes separately
modulating, using the optical modulator, in-phase and quadrature
components of the laser output, the optical modulator being a
polarization multiplexed in-phase and quadrature (PM-IQ)
modulator.
7. The method of claim 1, wherein the WDM transceiver module is a
non-coherent WDM transceiver module and the optical modulator is
not configured to modulate a phase component of the laser
output.
8. The method of claim 1, further comprising: monitoring, using a
power monitor operatively coupled to the optical modulator, an
optical power of the received laser output.
9. A method, comprising: receiving, at a control unit, data on a
first laser output transmitted by a wavelength division
multiplexing (WDM) transceiver module; receiving, at the control
unit, a second laser output from a laser source; analyzing the
first laser output and the second laser output to determine
information related to laser transmission conditions of the WDM
transceiver module; and generating a control message for
transmission to the laser source based on the determined
information.
10. The method of claim 9, wherein the laser source is an external
laser source and the WDM transceiver module does not include an
onboard laser source.
11. The method of claim 9, wherein the determined information
includes one or more of a power level of the second laser output
from the laser source, fiber loss during transmission of the second
laser output from the laser source, and alarm status of the WDM
transceiver module.
12. The method of claim 9, wherein the control message includes
instructions on an adjustment to a power level of the second laser
output prior to transmission to the WDM transceiver module by the
laser source.
13. The method of claim 9, further comprising: monitoring, using a
power monitor operatively coupled to the WDM transceiver module, a
power level of the first laser output.
14. The method of claim 9, further comprising: monitoring, using a
power monitor operatively coupled to the WDM transceiver module, a
power level of the first laser output, the WDM transceiver module
including a Mach-Zehnder modulator that is configured to generate
at least a portion of the first laser output data based on the
monitored power level.
15. The method of claim 9, wherein: the laser source is an external
laser source; and the control message is transmitted to the
external laser source via a control network coupled to the control
unit and the external laser source.
16. A method, comprising: receiving, at a control unit, data on
transmission of a laser output to a wavelength division
multiplexing (WDM) transceiver module by a laser source; generating
a control signal based at least in part on the received data; and
transmitting the control signal to the laser source, the
transmission of the laser output to the WDM transceiver module and
the transmission of the control signal to the laser source
occurring via a same bi-directional cable.
17. The method of claim 16, wherein the control signal is an
electrical signal and the bi-directional cable includes an
electrical wire for transmitting the electrical signal.
18. The method of claim 16, wherein the control signal is an
optical signal, and the laser output and the control signal are
transmitted via a same polarization maintaining optical fiber, the
bi-directional cable including the polarization maintaining optical
fiber.
19. The method of claim 16, wherein: the control signal is an
optical signal and the bi-directional cable includes a polarization
maintaining optical fiber; and the laser output and the control
signal are transmitted via a slow axis and a fast axis,
respectively, of the polarization maintaining optical fiber.
20. The method of claim 16, wherein: the control signal is an
optical signal, the laser output is an unmodulated laser beam, and
the bi-directional cable includes an optical fiber; and the laser
output and the control signal are transmitted out of band via the
optical fiber.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/485,202, filed Apr. 11, 2017, titled
"Optical Transceiver with External Laser Source," which is a
non-provisional of and claims priority under 35 U.S.C. .sctn. 119
to U.S. provisional application Ser. No. 62/408,316, filed Oct. 14,
2016, titled "Optical Transceiver with External Laser Source." Each
disclosure of the above applications is expressly incorporated
herein by reference in its entirety.
FIELD OF THE DISCLOSURE
[0002] This document pertains generally, but not by way of
limitation, to a wavelength division multiplexing (WDM) optical
transceiver module, and particularly, to a WDM optical transceiver
module that relies on a laser source that is external to the WDM
optical transceiver module.
BACKGROUND
[0003] It is difficult to meet the density and throughput demand on
the line cards operating with WDM optics, also called colored
optics or line optics. If WDM optics cannot meet such demands and
consequently are perceived as a waste of router switching capacity,
then grey optics--the alternative to WDM optics--may be connected
to third party external transponder shelves.
[0004] The gap between WDM optics and grey optics results from the
inclusion in WDM optics of at least one temperature controlled
tunable laser source. Such laser sources occupy a large part of WDM
optics such as WDM optical modules. For example, over 30% of the
real estate could be occupied by laser sources, such that the laser
sources set a floor on the size of WDM optical modules and a
ceiling on the density of WDM optical modules.
[0005] The laser source is often the only element of WDM optical
modules that requires a thermo-electric cooler (TEC). Thus compared
to other elements on the WDM optical module, the laser source
imposes the strictest requirements on the case temperature and heat
dissipation.
[0006] The laser source height is difficult to reduce. For example,
the integrated laser assembly height adds with the printed circuit
board assembly (PCBA) and prevents the assembly from fitting into
the 9.5 mm dimension of CFP8/CFP4 modules.
[0007] The laser source can consume, for example, more than 30% of
the power of WDM optical modules, including the TEC. Typical
numbers are about 3 W. Optimistic projections for the future are
around 2 W.
[0008] The optical power of micro-integrable tunable laser
assemblies (.mu.ITLA) in the modules can generate insufficient
optical power with acceptable power consumption, or else generate
sufficient optical power with unacceptable power consumption. An
optical amplifier may be required in order to overcome insufficient
optical power.
[0009] The laser source is not integrated in the
transmitter/receiver. The laser source is a separate chip coupled
with a fiber to the transmitter optical sub-assembly and receiver
optical sub-assembly (TOSA and ROSA). Prospective gains from
integration are limited in terms of size and power.
[0010] When WDM optics are a coherent transceiver, WDM optics also
include a very powerful DSP and power consuming optoelectronics
(e.g., a polarization multiplexed in-phase and quadrature (PM-IQ)
modulator with a quad-driver and 4 digital-to-analog converters
(DACs), and an integrated coherent receiver (ICR) paired with 4
receivers and 4 transimpedance amplifiers (TIAs)).
[0011] Due to the inclusion of such elements, it is difficult to
reduce the size and power consumption of WDM optics modules down to
grey optics modules. Low-power digital signal processing (DSP) and
low-power optics, integration on-board, and so on are all helpful
aspects that do not give a fundamental advantage to WDM optics;
when grey optics uses the same such technology, grey optics consume
less power and occupy less space than its WDM counterpart.
SUMMARY OF THE DISCLOSURE
[0012] Embodiments of the current disclosure include a wavelength
division multiplexing (WDM) transceiver module comprising an
optical port and an optical modulator operatively coupled to the
optical port. The optical port includes a data transmit optical
fiber connector and a data receive optical fiber connector; and a
laser source-in optical fiber connector configured to couple to a
laser source external to the WDM transceiver module, and provide
polarization alignment for a polarization-maintaining fiber. The
optical modulator may be operatively coupled to the optical port
and configured to receive a laser output from the external laser
source via the polarization-maintaining fiber and modulate the
laser output based on analog electrical signals generated by a
digital signal processor. In some embodiments, the WDM transceiver
module may not include an onboard laser source and may be
operatively coupleable to or capable of integrated into a host
board.
[0013] In some embodiments, the WDM transceiver module is
coupleable to the host board such that the WDM transceiver module
is pluggable into the host board. In some embodiments, the WDM
transceiver module is coupleable to the host board such the WDM
transceiver module is pluggable into the host board and does not
include the digital signal processor. Yet in some embodiments, the
WDM transceiver module is integrated into the host board.
[0014] In some embodiments, the optical port further includes an
optical pump-in optical fiber connector configured to couple to one
or more external optical pumps. The optical pump-in optical fiber
connector may include a specific-wavelength fiber, an operative
wavelength of the specific-wavelength fiber substantially matching
a wavelength of the optical pump laser.
[0015] In some embodiments, the WDM transceiver module may be a
coherent WDM transceiver module, and the optical modulator can be a
polarization multiplexed in-phase and quadrature (PM-IQ) modulator
configured to separately modulate in-phase and quadrature
components of the laser output. In some embodiments, the WDM
transceiver module may be a non-coherent WDM transceiver module and
the optical modulator may be or may not be configured to modulate a
phase component of the laser output.
[0016] In some embodiments, the WDM transceiver module may comprise
a power monitor operatively coupled to the optical modulator and
configured to monitor an optical power of the laser output received
from the external laser source.
[0017] In some embodiments of the current disclosure, a system
comprising a wavelength division multiplexing (WDM) transceiver
module and a control unit is disclosed. The WDM transceiver module
includes a laser source-in optical fiber connector configured to
receive a first laser output after transmission of a second laser
output from an external laser source external to the WDM
transceiver module. In some embodiments, the WDM transceiver module
may not include an onboard laser source and may be operatively
coupleable to a host board. The control unit may be configured to
receive a second laser output data from the external laser source
and a first laser output data from the WDM transceiver module. In
some embodiments, the control unit may be configured to: analyze
the first laser output data and the second laser output data so as
to determine information related to laser transmission conditions
of the WDM transceiver module; and generate a control message for
transmission to the external laser source based on the determined
information.
[0018] In some embodiments, the determined information includes one
or more of a power level of the second laser output from the
external laser source, fiber loss during transmission of the second
laser output from the external laser source, and alarm status of
the WDM transceiver module. Further, the control message may
include instructions on an adjustment to a power level of the
second laser output prior to transmission to the WDM transceiver
module by the external laser source. The control message is
transmitted to the external laser source via a control network
coupled to the control unit and the external laser source. In some
embodiments, the WDM transceiver module may comprise a power
monitor operatively coupled to the WDM transceiver module and
configured to monitor a power level of the first laser output. The
WDM transceiver module may include a Mach-Zehnder modulator that is
configured to generate at least a portion of the first laser output
data based on the monitored power level.
[0019] In some embodiments of the current disclosure, a system
comprising a wavelength division multiplexing (WDM) optical
transceiver module and a control unit is disclosed. The WDM optical
transceiver module may be configured to receive a laser output
transmitted by an external laser source external to the WDM
transceiver module and the module may not include an onboard laser
source. In some embodiments, the control unit may be configured to
receive data related to transmission of the laser output to the WDM
transceiver module. Further, the control unit may be configured to
generate a control signal based at least in part on the received
data, and may transmit the control signal to the external laser
source. In some embodiments, the transmission of the laser output
to the WDM transceiver module and the transmission of the control
signal to the external laser source occur via a same bi-directional
cable.
[0020] In some embodiments, the control signal may be an electrical
signal and the bi-directional cable may include an electrical wire
for transmitting the electrical signal. In some embodiments, the
control signal may be an optical signal, and the laser output and
the control signal may be transmitted via the same polarization
maintaining optical fiber, the bi-directional cable including the
polarization maintaining optical fiber. In some embodiments, the
laser output and the control signal may be transmitted via a slow
axis and a fast axis, respectively, of the polarization maintaining
optical fiber. In some embodiments, the control signal is an
optical signal, the laser output is an unmodulated laser beam, and
the bi-directional cable includes an optical fiber. Further, the
laser output and the control signal may be transmitted out of band
via the optical fiber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In the drawings, which are not necessarily drawn to scale,
like numerals may describe similar components in different views.
Like numerals having different letter suffixes may represent
different instances of similar components. The drawings illustrate
generally, by way of example, but not by way of limitation, various
embodiments discussed in the present document.
[0022] FIGS. 1-2 are diagrams showing general examples of a WDM
optical transceiver module.
[0023] FIG. 3 is a diagram of an example of a WDM optical
transceiver module coupled in between a host board an optical fiber
ribbon cable.
[0024] FIGS. 4-5 are diagrams showing examples of the connector in
between the WDM optical transceiver module and the optical fiber
ribbon cable.
[0025] FIGS. 6A-B show a diagram showing a general example of an
access node chassis with a WDM optical transceiver module (FIG. 6A)
and a module with two separate connectors, one for receiving TX/RX
fibers and another for receiving polarization-maintaining ones
(FIG. 6B).
[0026] FIG. 7 is a diagram showing an example process flow of the
WDM optical transceiver module in the access node.
[0027] FIG. 8 is a diagram showing another example of the connector
in between the WDM optical transceiver module and the optical fiber
cable.
[0028] FIG. 9 is a diagram of an example of a WDM optical
transceiver module with an external laser source and external
optical pump.
[0029] FIGS. 10-12 are diagrams showing the WDM optical transceiver
module and the host board.
DETAILED DESCRIPTION
[0030] In example embodiments, a WDM optical transceiver module
relies on an external laser source. For example, the WDM optical
transceiver module can be operatively coupled to and receive laser
power from a laser source that is external to the module itself. In
such embodiments, the WDM optical transceiver module may not have
any laser source onboard the module itself. In other embodiments,
the WDM optical transceiver module can have a laser source onboard,
and yet can also be operatively coupled to and receive laser power
from an external laser source. The embodiments where the module
does not have a laser source onboard (and instead relies solely on
an external laser source) have the advantages of a WDM optical
transceiver module without the bulk and the temperature-related and
heat-dissipation-related strict requirements on the module case (or
housing or form) that come about due to the inclusion of the laser
source in the WDM optical transceiver module. Further, other
elements or components that usually accompany the laser source such
as thermos-electric coolers (TECs) can also be removed from the WDM
optical transceiver module when the module does not have an onboard
laser source and relies on an external laser source. In some
embodiments, the lack of a laser source (and associated elements
such as TECs) from a WDM optical transceiver module allows for an
appreciable reduction in size and power consumption of the module
during operation.
[0031] Examples of WDM optical transceiver modules include: digital
pluggable modules (e.g., digital coherent optics (DCO) pluggable
modules like the Acacia 100G C form-factor pluggable (CFP) AC100M
or direct detect optics like the Inphi ColorZ 100GBE-QSFP28-WDM2);
analog pluggable modules (e.g., analog coherent optics (ACO)
pluggable modules like the CFP2-ACO used on Juniper line cards on
the PTX and MX platforms, PTX-5-100G-WDM and MIC3-100G-DWDM
respectively); multi-source agreement (MSA) modules; on-board
optics (e.g. Optical Internetworking Forum (OIF) 2016.301.00); and
other WDM optic assemblies.
[0032] FIGS. 1-2 are diagrams showing general examples of a WDM
optical transceiver module. FIG. 1 is a diagram of WDM optical
transceiver module 200 with optical fiber connectors 210 and host
board connector 220. Optical fiber connectors 210 includes multiple
connectors for multiple optical fibers, including transmit data
optical fiber connector 212, laser source in optical fiber
connector 214, and receive data optical fiber connector 216. WDM
optical transceiver module 200 is coupled to a laser source via
laser source in optical fiber connector 214. As a result, some
embodiments of the WDM optical transceiver module 200 rely on a
laser source external to the WDM optical transceiver module 200. In
such embodiments, the WDM optical transceiver module 200 may or may
not have a laser source in the WDM optical transceiver module 200
itself.
[0033] FIG. 2 is a diagram of WDM optical transceiver module 202
similar to WDM optical transceiver module 200. Optical fiber
connectors 211, compared to optical fiber connectors 210, adds
optical pump in optical fiber connector 218. WDM optical
transceiver module 202 is coupled to an optical pump via optical
pump in optical fiber connector 218. As a result, some embodiments
of the WDM optical transceiver module 202 rely on an optical pump
external to the WDM optical transceiver module 202. In such
embodiments, the WDM optical transceiver module 200 may or may not
have a laser source in the WDM optical transceiver module 200
itself.
[0034] In typical optical transport networks, the optical signal
between two WDM optical transceiver modules is transmitted over
fiber pairs. In an example implementation one or multiple modules,
such as tens or hundreds, are connected to an optical node formed
by a combination of programmable or fixed multiplexers, optical
amplifiers, filters, attenuators, and so on. The optical signals
are combined together, optically amplified, and sent all together
on the same fiber pair over several tens of kilometers. Every 50 km
or so there is an optical amplifier. In a submarine system
implementation, signals can travel up to 12,000 km through hundreds
of amplifiers. In meshed terrestrial networks, the signals can
travel through multiple optical nodes. At each node, each one of
the signals that came from the same fiber pair can be sent toward
different directions. At the destination node optical signals are
demultiplexed and another optical module receives the desired
optical signal.
[0035] WDM optical transceiver module is coherent or non-coherent,
using phase information or not. Coherent modules can carry 100 Gb/s
and beyond over long distances. A recent example of an application
of non-coherent modules limited to very short WDM links, below 100
km, was based on direct-detect PAM modulation formats with DSP
based equalization. In some embodiments, the WDM transceiver module
may be a non-coherent WDM transceiver module, and such a
transceiver module can comprise an optical modulator that may or
may not be configured to modulate a phase component of the laser
output.
[0036] WDM optical transceiver module is pluggable vs on-board,
referring to how the module is connected to the host. The module
can be placed on a line card in a factory, like a 100G MSA module.
Or, the module can be a pluggable module, like CFP MSA.
[0037] A coherent WDM optical transceiver module is analog coherent
optics or digital coherent optics (ACO or DCO). DCO includes
powerful digital signal processing (DSP). DCO receives digital data
and the DSP generates the analog signals that are sent toward the
electro-optical converters. Also the DSP receives the analog
signals from the opto-electrical converters, demodulate the RX
signal, and sends to the host the digital data signals. The DSP is
in the module. The interface is an often-standardized digital
interface, such as CAUI-4. In the case of ACO the DSP sits on the
host and the interface is a connector on top of which the analog
signals are transported. A WDM optical module, when it is
pluggable, can include or not include the DSP.
[0038] Some embodiments of a WDM optical transceiver module
include, but are not limited to:
[0039] Non-coherent and pluggable;
[0040] Non-coherent and on-board;
[0041] Digital, coherent, and pluggable;
[0042] Digital, coherent, and on-board; and
[0043] Analog, coherent, and pluggable;
[0044] A coherent WDM optical transceiver module encodes and
decodes; and transmits and receives an electrical signal that is
converted to and from an optical signal that transits the optical
fibers of an optical transport system. A coherent WDM optical
transceiver module includes a transmitter and receiver.
[0045] The transmitter has one or more of the following
elements:
[0046] A digital signal processor (DSP) that receives and processes
a series of digital signals. The process includes: encoding,
mapping, digital filtering, equalization, and lead to the
generation at the output of the digital-to-analog converters of a
series of analog electrical signals.
[0047] A driver that amplifies the analog electrical signals in
order to achieve the required peak-to-peak output to meet the
modulator's needs. The driver is a multi-channel element, with a
dedicated amplifier for each analog electrical signal.
[0048] An optical modulator that receives an unmodulated laser
source from outside the WDM optical transceiver module through a
polarization maintaining fiber and modulates the laser based on the
analog electrical signals received from the DSP or directly from
the host in case of--ACO optics. If the module is coherent the
modulator can be a polarization multiplexed complex modulator
(PM-IQ) that typically has 4 input signals for separately
modulating the in-phase (I) and quadrature (Q) components of each
one of the two orthogonal polarizations (often referred to as H/V
or X/Y) of the light. The modulator takes care of the necessary
polarization rotation between the X and Y signals to form a
polarization multiplexed optical signal. If the module is
non-coherent the modulator can be a traditional Mach-Zehnder
modulator or a phase modulator or an IQ modulator. The first two
uses one analog signal and an IQ modulator uses two analog
signals.
[0049] Signal conditioning elements can be before, after, or both
before and after the modulator. Example elements are optical
amplifiers (e.g., semiconductor optical amplifiers or erbium doped
fiber amplifiers), variable optical attenuators, shutters, or
optical filters.
[0050] Signal telemetry element like power taps that allow for
capturing a calibrated small amount of a light in order to measure
the optical power. At least one power monitor measures the incoming
light from the external laser source in addition to other ones in a
module.
[0051] If more than one optical carrier is modulated in the module,
such that multiple laser sources are coming from outside and
multiple optical modulators are present, then there can also be a
multiplexer in the form of an optical interleaver, an optical
coupler, or an arrayed waveguide multiplexer (AWG).
[0052] One or multiple optical TX ports where the transmitted
signal(s) are sent to the optical transport system. Embodiments of
the transmitter generally include one or multiple optical TX
ports.
[0053] Control logic for the driver, modulator biasing points,
other elements, and power supplies. Embodiments of the transmitter
generally include control logic.
[0054] Some embodiments of the transmitter include, but are not
limited to:
[0055] DSP;
[0056] Driver;
[0057] Optical modulator;
[0058] Signal conditioning elements;
[0059] Signal telemetry element;
[0060] Multiplexer;
[0061] DSP and driver;
[0062] DSP and optical modulator;
[0063] DSP and signal conditioning elements;
[0064] DSP and signal telemetry element;
[0065] DSP and multiplexer;
[0066] Driver and optical modulator;
[0067] Driver and signal conditioning elements;
[0068] Driver and signal telemetry element;
[0069] Driver and multiplexer;
[0070] Optical modulator and signal conditioning elements;
[0071] Optical modulator and signal telemetry element;
[0072] Optical modulator and multiplexer;
[0073] Signal conditioning elements and signal telemetry
element;
[0074] Signal conditioning elements and multiplexer;
[0075] Signal telemetry element and multiplexer;
[0076] DSP, driver, and optical modulator;
[0077] DSP, driver, and signal conditioning elements;
[0078] DSP, driver, and signal telemetry element;
[0079] DSP, driver, and multiplexer;
[0080] DSP, optical modulator, and signal conditioning
elements;
[0081] DSP, optical modulator, and signal telemetry element;
[0082] DSP, optical modulator, and multiplexer;
[0083] DSP, signal conditioning elements, and signal telemetry
element;
[0084] DSP, signal conditioning elements, and multiplexer;
[0085] DSP, signal telemetry element, and multiplexer;
[0086] Driver, optical modulator, and signal conditioning
elements;
[0087] Driver, optical modulator, and signal telemetry element;
[0088] Driver, optical modulator, and multiplexer;
[0089] Driver, signal conditioning elements, and signal telemetry
element;
[0090] Driver, signal conditioning elements, and multiplexer;
[0091] Driver, signal telemetry element, and multiplexer;
[0092] Optical modulator, signal conditioning elements, and signal
telemetry element;
[0093] Optical modulator, signal conditioning elements, and
multiplexer;
[0094] Signal conditioning elements, signal telemetry element, and
multiplexer;
[0095] DSP, driver, optical modulator, and signal conditioning
elements;
[0096] DSP, driver, optical modulator, and signal telemetry
element;
[0097] DSP, driver, optical modulator, and multiplexer;
[0098] DSP, driver, signal conditioning elements, and signal
telemetry element;
[0099] DSP, driver, signal conditioning elements, and
multiplexer;
[0100] DSP, driver, signal telemetry element, and multiplexer;
[0101] DSP, optical modulator, signal conditioning elements, and
signal telemetry element; and
[0102] DSP, optical modulator, signal conditioning elements, and
multiplexer;
[0103] DSP, optical modulator, signal telemetry element, and
multiplexer;
[0104] DSP, signal conditioning elements, signal telemetry element,
and multiplexer;
[0105] Driver, optical modulator, signal conditioning elements, and
signal telemetry element;
[0106] Driver, optical modulator, signal conditioning elements, and
multiplexer;
[0107] Driver, signal conditioning elements, signal telemetry
element, and multiplexer;
[0108] Optical modulator, signal conditioning elements, signal
telemetry element, and multiplexer;
[0109] DSP, driver, optical modulator, signal conditioning
elements, and signal telemetry element;
[0110] DSP, driver, optical modulator, signal conditioning
elements, and multiplexer;
[0111] DSP, driver, optical modulator, signal telemetry element,
and multiplexer;
[0112] DSP, driver, signal conditioning elements, signal telemetry
element, and multiplexer;
[0113] DSP, optical modulator, signal conditioning elements, signal
telemetry element, and multiplexer;
[0114] Driver, optical modulator, signal conditioning elements,
signal telemetry element, and multiplexer;
[0115] DSP, driver, optical modulator, signal conditioning
elements, signal telemetry element, and multiplexer;
[0116] The receiver has one or more of the following elements:
[0117] RX optical port(s) that receives one or multiple optical
signal(s) from the optical transport system. Embodiments of the
transmitter generally include one or multiple RX optical ports.
[0118] Optical signal conditioning elements such as a variable
attenuator, optical amplifier, shutter, optical filter, and so
on.
[0119] In a coherent embodiment, for each signal a coherent mixer
for each polarization that creates beating between the received
signal and a local oscillator that comes from outside the WDM
optical transceiver module. For example, the local oscillator is
from the TX laser source that comes from outside the WDM optical
transceiver split between TX and RX with a polarization maintaining
splitter. In general a polarization beam splitter splits the RX
signal among the two coherent mixers, one per polarization. A
non-coherent embodiment can omit the mixer.
[0120] Photodiodes, such as 2 per mixer, for a total of 4 per
polarization. An embodiment has balanced photodiodes that are pairs
of photodiodes in a specific configuration. The photodiodes convert
the optical signal into an analog electrical signal. For a
non-coherent embodiment a single photodiode is sufficient.
[0121] Electrical amplifiers for the analog electrical signal,
typically trans-impedence amplifiers (TIA). Typically 4 for each
received signal (IQ/XY). For non-coherent a single amplifier is the
minimum.
[0122] Analog-to-digital converter and digital signal processing
(DSP) that performs a long series of operations: equalization, time
recovery, chromatic dispersion compensation, polarization
demultiplexing, carrier phase and frequency recovery, demodulation,
and decoding. For a non-coherent embodiment the list is generally
shorter, such as equalization and time recovery. For--ACO the DSP
is not on the module so the module finishes with the signal output
from the electrical TIA.
[0123] Control logic for the element, such as a power monitor on
the received power from the laser source if the transmit laser
source is not shared. Embodiments of the receiver generally include
control logic.
[0124] Some embodiments of the receiver include, but are not
limited to:
[0125] Optical signal conditioning elements;
[0126] Coherent mixers;
[0127] Photodiode(s);
[0128] Electrical amplifiers;
[0129] Analog-to-digital converter and DSP;
[0130] Optical signal conditioning elements and coherent
mixers;
[0131] Optical signal conditioning elements and photodiode(s);
[0132] Optical signal conditioning elements and electrical
amplifiers;
[0133] Optical signal conditioning elements and analog-to-digital
converter and DSP;
[0134] Coherent mixers and photodiode(s);
[0135] Coherent mixers and electrical amplifiers;
[0136] Coherent mixers and analog-to-digital converter and DSP;
[0137] Photodiode(s) and electrical amplifiers;
[0138] Photodiode(s) and analog-to-digital converter and DSP;
[0139] Electrical amplifiers and analog-to-digital converter and
DSP;
[0140] Optical signal conditioning elements, coherent mixers, and
photodiode(s);
[0141] Optical signal conditioning elements, coherent mixers, and
electrical amplifiers;
[0142] Optical signal conditioning elements, coherent mixers, and
analog-to-digital converter and DSP;
[0143] Optical signal conditioning elements, photodiode(s), and
electrical amplifiers;
[0144] Optical signal conditioning elements, photodiode(s), and
analog-to-digital converter and DSP;
[0145] Optical signal conditioning elements, electrical amplifiers,
and analog-to-digital converter and DSP;
[0146] Coherent mixers, photodiode(s), and electrical
amplifiers;
[0147] Coherent mixers, photodiode(s), and analog-to-digital
converter and DSP;
[0148] Coherent mixers, electrical amplifiers, and
analog-to-digital converter and DSP;
[0149] Photodiode(s); electrical amplifiers, and analog-to-digital
converter and DSP;
[0150] Optical signal conditioning elements, coherent mixers,
photodiode(s), and electrical amplifiers;
[0151] Optical signal conditioning elements, coherent mixers,
photodiode(s), and analog-to-digital converter and DSP;
[0152] Optical signal conditioning elements, coherent mixers,
electrical amplifiers, and analog-to-digital converter and DSP;
[0153] Optical signal conditioning elements, photodiode(s),
electrical amplifiers and analog-to-digital converter and DSP;
[0154] Coherent mixers, photodiode(s), electrical amplifiers, and
analog-to-digital converter and DSP;
[0155] Optical signal conditioning elements, coherent mixers,
photodiode(s), electrical amplifiers, and analog-to-digital
converter and DSP;
[0156] FIG. 3 is a diagram of an example of a WDM optical
transceiver module coupled in between a host board an optical fiber
ribbon cable. WDM optical transceiver module 300 has a first
connector 302 such as a multi-fiber push on (MPO) connector and a
second connector 304 to host board 310. First connector 302 is an
optical port connected to the rest of the optical network.
[0157] In some implementations the WDM optical transceiver module
300, which may not have a laser source in the WDM optical
transceiver module 300 itself, is coupled to a laser source via
first connector 302. In other words, the first connector 302 may
connect the WDM optical transceiver module 300 to both an optical
network and a laser source that is external to the WDM optical
transceiver module 300. For example, the first connector 302 can be
configured to receive or be connected to a ribbon fiber patch cable
320 that contains different types of fibers, one of which carries
one type of laser beam. For example, a ribbon fiber patch cable 320
may contain one or more of different types of fibers such as but
not limited to single mode fibers, polarization maintaining fibers
and pump laser fibers, respectively corresponding to standard
optical signals, unmodulated continuous wave (CW) laser source
beams and pump laser beams. In other embodiments the WDM optical
transceiver module 300 is coupled to a laser source via a connector
other than first connector 302 (e.g., instead of or in addition to
being connected via the first connector 302).
[0158] In some embodiments the WDM optical transceiver module 300
is coupled to an optical pump via first connector 302. In other
embodiments the WDM optical transceiver module 300 is coupled to an
optical pump via a connector other than first connector 302 (e.g.,
instead of or in addition to being connected via the first
connector 302).
[0159] Second connector 304 is an electrical connector that carries
data and control signals between WDM optical transceiver module 300
and host board 310. Such data signals can be digital or analog.
[0160] FIGS. 4-5 are diagrams showing examples of the connector in
between the WDM optical transceiver module and the optical fiber
ribbon cable. In FIG. 4, MPO connector 404 connects 4 channels,
including 1 laser source per channel. MPO connector 404 connects 4
transmit single mode optical fibers (SMF) 430, 4 laser source
polarization maintaining optical fibers (PMF) 440, and 4 receive
SMF 450.
[0161] In FIG. 5, MPO connector 504 connects 2 channels, including
2 laser sources per channel and an optical pump per channel. MPO
connector 504 connects 2 transmit SMF 530, 4 laser source PMF 540,
2 receive SMF 550, a transmit optical pump optical fiber 560, and a
receive optical pump optical fiber 562.
[0162] In FIGS. 4-5, the MPO connector is an optical port made of
multiple varieties of optical fibers including single mode fibers,
polarization maintaining fibers, and pump laser fibers (e.g.
HI-1060). The optical port can be an MPO connector, or another
connector, that is used to connect a ribbon fiber cable. The fibers
in the ribbon are different varieties including single mode fibers,
polarization maintaining fibers, and pump laser fibers. The fiber
used for modulated optical signal can be single mode or multi-mode.
The fibers of the unmodulated continuous wave (CW) laser source are
polarization maintaining fibers. The optional fibers of the pump
lasers are fibers designed for that specific pump laser
wavelengths, for example HI-1060 for 980 nm pump lasers. Other
embodiments vary the number of channels, the total number of
fibers, and the number of fibers of each variety of fiber. For
example, in some embodiments, the number of channels can be 1, 2,
3, 4, 5, 6, 7 or 8.
[0163] It should be noted that, in any of the embodiments discussed
herein, the disclosed fibers can be attached to the module via any
number of connectors. For example, as in the example embodiments
discussed above, the fibers may be attached to the module via a
single connector. In some embodiments, however, a plurality of
connectors may be used and the fibers maybe bundled or groups into
separate sets and each set may use a dedicated connector selected
from the plurality of connectors to connect to the module. For
example, it would be possible to maintain a legacy compatibility to
existing systems by using a connector for TX/RX fibers only (for
example, as existing modules with internal laser sources) and in
addition a second connector may be used for connecting the laser
sources through polarization maintaining fibers.
[0164] FIG. 6 is a diagram showing a general example of an access
node chassis with a WDM optical transceiver module. Access node
chassis 600 includes control unit 610 coupled to control network
640; and line cards 620, 622, and 624. Line card 622 includes WDM
optical transceiver optical modules, including WDM optical
transceiver optical module 638, with optical fiber connectors 630,
632, 634, and 636. Optical fiber connector 630 is coupled to a
laser source 650 in an external chassis distinct from access node
chassis 600. In some implementations, the WDM optical transceiver
module 638 may not have an onboard laser source. Communication
devices or components within the chassis of the laser source can
also be coupled to control network 640, allowing communication
between the laser source 650 and the control unit 610 to take
place. In some implementations, the control unit 610 may not be
coupled to the control network 640, or it may be coupled to the
control network 640 in addition to being coupled to a cable (not
shown) that may be used to transmit control messages between the
control unit 610 and the laser source 650.
[0165] In some implementations, the control unit 610 may be used to
control and regulate the amount of laser power that comes from the
external laser source 650 to the WDM optical transceiver module
638. In particular, due to reasons such as the fiber loss, etc.,
the amount of laser power that arrives at the WDM optical
transceiver module 638 may be different or even significantly
different than the power of the laser beam transmitted by the laser
source 650 (i.e., the power of the laser beam received by the WDM
optical transceiver module 638 may not be at least substantially
same as the desired or intended amount of power to be received by
module 638). In such instances, the control unit 610 may receive
data related to the characteristics of the laser beam generated and
transmitted by the laser source 650 and the characteristics of the
laser beam received by the WDM optical transceiver module 638, the
characteristics including for example power level or range,
wavelength range, etc. of each laser beam. For example, the WDM
optical transceiver module 638 may include photodiodes for
measuring the power levels of the received beams. Upon receiving
these data, in such implementations, the control unit 610 may
determine the proper calibration for the transmission of the laser
power and generate control messages for sending to the laser source
650 to request adjustment to one or more characteristics of the
laser beam being generated and transmitted by the laser source 650.
For example, the control messages may request an increase in the
generation and transmission of the power of the laser beam from the
laser source 650 so as to compensate for losses that occur during
transmission. In some implementations, this may occur on a
continuous basis (or near-continuous basis, repeated basis,
periodic basis, etc.) during the operation of the WDM optical
transceiver module 638.
[0166] In some implementations, the transmission of signals
carrying the control messages and/or the data between the external
laser source 650 and the control unit 610 or the WDM optical
transceiver module 638 (or generally the access node chassis 600
that includes the control unit 610 and the line card 622, which in
turn includes the WDM optical transceiver module 638) may occur via
a control network 640 to which both the control unit 610 and the
communication devices or components within the chassis of the
external laser source 650 are coupled. In some implementations,
however, the messaging may not occur via a control network, and
instead the data and messages may be exchanged via the cable that
is used to couple the external laser source 650 to the WDM optical
transceiver module 638 (via the line card 622, for example). In
some implementations, dedicated transmitter/receiver may be used
for these data/control messages, but in some cases, it may be
preferable not to use the devices of the same kind as those already
employed by the WDM module for high data rate communication in
order to reduce the size and power consumption of the WDM optical
transceiver module 638. In some embodiments, electrical
connectivity may be established via a cable which shall include
electrical wires capable of low-speed communication (like a serial
or SPI bus). In some embodiments, a source generator may be
utilized to add some slow modulation (e.g., dithering tone or AM
modulation) by driving with a slow signal the laser current supply.
The receiver could then pair the tap power monitor to an electrical
device that could decode such information.
[0167] In some implementations, the cable that couples the laser
source, and carries the laser beam, to the WDM optical transceiver
module 638 may be a cable capable of carrying the signals carrying
the control messages and data exchanged between the laser source
650 and the module 638 in a bi-directional manner. In some other
implementations, the cable may be used as previously proposed as
uni-directional. In the implementations where the cable is capable
of carrying electrical signals in addition to optical signals, the
cable may include at least one electrical wire (in addition to
optical fibers, for example) and the signals carrying the control
messages/data may travel via the at least one electrical wire. In
such implementations, the nature of the signals carrying the
control messages/data may be electrical. In the embodiments where
the signals carrying the control messages/data are optical, the
signals carrying the control messages/data may travel in dedicated
optical fibers that are different from the optical fibers used to
transport the laser beam (e.g., unmodulated continuous wave signal)
that is being generated and transmitted by the external laser
source 650 to the WDM optical transceiver module 638. In some
implementations, the control messages/data may be exchanged via the
same optical fibers as those used by the laser beam from the laser
source 650, and in such embodiments different techniques may be
used to avoid or minimize the interference between the laser beam
and the signals carrying the control messages/data.
[0168] In some implementations, a pilot signal may be used for the
control messages/data with little or no perturbation of the laser
beam (its amplitude, for example). For example, the pilot signal
may be used to slowly change the power of the laser beam (hence,
little or no perturbation to the laser beam) as the laser beam
travels from the laser source 650 to the WDM optical transceiver
module 638. In such implementations, the pilot signal carrying the
control messages/data and the laser beam may be travelling on the
same optical fiber but with little or no interference. Upon arrival
at the WDM optical transceiver module 638, in some instances, the
control unit 610 may determine the power of the received laser beam
(e.g., using a power monitor that uses photodiodes) as well as the
power of the laser beam generated by the external laser source 650
prior to transmission (e.g., from the data) so as to determine the
laser beam adjustments that may be performed to receive a laser
beam of desired characteristics. Example of such adjustments
include adjustments in power levels, wavelength ranges, etc. In
such implementations, the control unit 610 may then generate
control messages requesting such adjustments and transmit the
messages back to the laser source 650 in similar manner as
described for transmission from the laser source to 650 the WDM
optical transceiver module 638. In some implementations, back
reflectors (that are adjustable so that control messages/data can
be imparted) are located in the WDM optical transceiver module 638
and can be used to send signals back to the external laser source
650. In some embodiments, the laser beam and the control messages
may be transmitted and received via signals of different
wavelengths.
[0169] In some implementations, the optical fibers carrying the
laser beam from the laser source 650 (e.g., an unmodulated CW laser
source) may be polarization maintaining fibers, which may have
so-called fast axis and slow axis. In such implementations, the
control messages/data may be transmitted for example via the fast
axis and the laser beam from the laser source 650 may be
transmitted for example via the soft axis; as such, the control
messages/data and the laser beam may be transmitted independently
from each other, leading to little or no perturbation of the laser
beam by the signal carrying the control messages/data. Upon arrival
at the access node chassis 600, in such implementations, the
signals carrying the control messages/data (e.g., on the fast axis)
may be fed into the control unit 610 and the laser beam (e.g., on
the slow axis) may be fed into the WDM optical transceiver module
638. In such implementations, the control unit 610 may proceed with
the determination of the appropriate adjustments and the generation
of further control messages as described above. An example
embodiment illustrating the generation of a control message to
adjust some characteristics of the laser generated and transmitted
by the laser source 650 is provided with reference to FIG. 7.
[0170] FIG. 7 is a diagram showing an example process flow of the
WDM optical transceiver module in the access node. The control loop
controls the correct start-up and operation of the WDM optical
transceiver optical module, including activation of laser source in
the correct conditions. The control loop includes a supply of the
laser source 650, control unit 610, and WDM optical transceiver
optical module 638. At 702 the control loop starts. At 704 the
control unit gets data from the source supply and the WDM optical
transceiver optical module 638. The control path splits into two
paths. In a first path, at 706 the supply of the laser source
collects CW set power and CW power range. At 708 the supply of the
laser source sends the collected data to the control unit. The
exchange of data and control messages between the source supply of
the laser source 650 and the control unit 610 may occur in any of
the manners discussed above. In a second path, at 712 the WDM
optical transceiver optical module collects data from power
monitors of CW power of the laser source received at the WDM
optical transceiver optical module. At 714 the WDM optical
transceiver optical module sends the collected data to the control
unit. The two paths merge again. At 710 the control unit waits and
receives the collected data from 708 and 714. AT 716 the control
unit calculates alarm conditions, fiber loss, and a new power set
point. At 718 the control unit sends the new desired
characteristics of the laser such as power target to the supply of
the laser source. At 720 the supply of the laser source sets the
new power set point for the laser source. At 722, the control unit
repeats.
[0171] In one embodiment the WDM optical transceiver module is
wavelength agnostic. To maintain accuracy in the power monitor of
the wavelength agnostic module, active control loops set the bias
of the Mach-Zehnder (MZ) modulator.
[0172] In another embodiment the WDM optical transceiver module has
registers for the configuration of the wavelength, and control
logic accesses the information. Knowing the wavelength allows for
retrieving the bias information for the MZ modulator from a lookup
table pre-populated during manufacturing and makes the power
monitor reading more accurate.
[0173] FIG. 8 is a diagram showing another example of the connector
in between the WDM optical transceiver module and the optical fiber
cable. The connector, such as an MPO connector or a series of line
card (LC) connectors or other compact optical connectors, is an
optical port made of multiple varieties of optical fibers including
single mode fibers, polarization maintaining fibers, and pump laser
fibers (e.g. HI-1060). The fiber used for modulated optical signal
can be single mode or multi-mode. The fibers of the unmodulated
continuous wave (CW) laser source are polarization maintaining
fibers. The optional fibers of the pump lasers are fibers designed
for that specific pump laser wavelengths, for example HI-1060 for
980 nm pump lasers. In some embodiments, standard single mode
fibers may be used for pumps lasers, and these may result in some
losses, which may not be significant for short fibers. Other
embodiments vary the number of channels, the total number of
fibers, and the number of fibers of each variety of fiber.
[0174] Example form factors of the WDM optical transceiver module
are discussed. Example embodiments are a coherent analog pluggable
optic. Example form factors are the CFP4 form factor 804 and the
CFP2 form factor 802. The laserless CFP4-ACO removes the laser.
Around 30% of the footprint is saved, the biggest height constraint
is removed, and more power is left for the TOSA and ROSA.
[0175] Various embodiments have an MPO connector in the front or a
line card (LC) connector. An example connector has the typical
transmit (TX) and receive (RX) fibers and PM fibers that carry the
CW laser source light. The CW laser source is split at the WDM
optical transceiver module into signal and local oscillator paths,
or multiple laser sources are coupled which helps meet the required
TX power.
[0176] FIG. 9 is a diagram of an example of a WDM optical
transceiver module with an external laser source and external
optical pump. WDM optical transceiver optical module 900 has
optical fiber connector 902 that connects to ribbon fiber patch
cable 920. Optical fiber connector 902 has a variety of fibers for
each channel. A first channel has transmit and receive single mode
fibers, polarization maintaining fiber of the laser source, and
pump laser fiber. A second channel also has transmit and receive
single mode fibers, polarization maintaining fiber of the laser
source, and pump laser fiber.
[0177] In a first channel, polarization maintaining splitter 946
splits a first laser source between TOSA 942 and ROSA 944. TOSA 942
and ROSA 944 include respective photodiodes to measure the power of
the outputs of polarization maintaining splitter 946. TOSA 942 is
coupled to an input of remotely pumped Erbium-Doped Fiber
Amplifiers (EDFA) 940. Remotely pumped EDFA 940 is coupled to an
optical pump from the optical fiber connector 902. Remotely pumped
EDFA 940 pumps the input received TOSA 942 and provides a pumped
output to the optical fiber connector 902.
[0178] A second channel is similar to the first channel, with
polarization maintaining splitter 956, TOSA 952, ROSA 954, and
remotely pumped EDFA 950. Controller 960 is coupled to the
photodiodes of TOSA 942, ROSA 944, TOSA 952, and ROSA 954.
Controller 960 collects the monitored powers from the photodiodes
and send the data back to a control unit as shown in FIG. 7.
[0179] FIG. 10 is a block diagram illustrating pluggable photonics
module 10 coupled to host board 28 in accordance with one or more
examples such as any of FIGS. 1-9. The combination of pluggable
photonics module 10 and host board 28 may be referred to as a
network device. Host board 28 is referred to as a host board in
that it "hosts" pluggable photonics module 10. That is, pluggable
photonics module 10 may be a removable front end module that may be
physically received by and removed from host board 28 operating as
a back end module within a communication system or device.
Pluggable photonics module 10 and host board 28 typically are
components of an optical communication device or system (e.g., a
network device) such as a wavelength-division multiplexing (WDM)
system, including a dense wavelength division multiplexing (DWDM)
system. For example, a WDM system may include a plurality of slots
reserved for a plurality of boards, such as host board 28. Each
host board 28 may receive one or more removable "pluggable"
photonics module 10 to provide optical connectivity for one or more
optical links 30. However, aspects are not limited to WDM systems.
For purposes of illustration only and for ease of description, the
examples are described in context of a WDM system.
[0180] In a WDM system, host board 28 or another board connected to
host board 28 receives lower data rate optical or electrical
signals from multiple devices such as switches or routers that host
board 28 or the other board serializes together into higher data
rate electrical signals. Pluggable photonics module 10 converts the
electrical signals to an optical signal for further transmission
into network 32 via optical link 30. Examples of network 32
include, but are not limited to, a wide area network (WAN) or the
Internet.
[0181] In the reverse, pluggable photonics module 10 receives
higher data rate optical signals via optical link 30 from network
32, and converts the optical signals to electrical signals. Host
board 28 receives the electrical signals from pluggable photonics
module 10, and host board 28 or the other board deserializes the
electrical signals into a plurality of lower data rate optical or
electrical signals for transmission to the routers and
switches.
[0182] As the amount of data that needs to be transmitted to and
received from network 32 increases, the data rate at which host
board 28 needs to forward data to and from the routers and switches
increases. For example, routers and switches are designed to
receive and transmit data at ever higher data rates, and the WDM
systems scale to the higher data rates to keep pace with data rates
from the routers and switches. For instance, some versions of host
board 28 and pluggable photonics module 10 operate at approximately
10 gigabits per second (Gbps), and other versions operate at 100
Gbps.
[0183] Scaling from 10 Gbps to 100 Gbps presents several design and
cost challenges. For example, 10 Gbps data rate is sufficiently
slow to allow simple modulation schemes such as on-off keying
(OOK), sometimes referred to as non-return-to-zero (NRZ)
modulation. In OOK modulation, the presence of a carrier wave for a
specific duration represents a binary one, and its absence for the
same duration represents a binary zero. However, OOK modulation may
not be suitable at 100 Gbps, and more complex modulation schemes
may be necessary. For example, hardware components may not be able
to process OOK modulated data at the relatively high rate of 100
Gbps.
[0184] In some examples, 100 Gbps may require phase-shift keying
(PSK) such as quadrature phase-shift keying (QPSK), as one example,
although other modulation schemes are possible such as binary
phase-shift keying (BPSK), polarization multiplexed BPSK (PM-BPSK,
polarization multiplexed QPSK (PM-QPSK), M-quadrature amplitude
modulation (M-QAM) (where M>4), or PM-M-QAM. For purposes of
illustration, the example techniques are described with respect to
QPSK modulation, and in particular PM-QPSK modulation. However,
aspects of this disclosure should not be considered so limiting.
The techniques are extendable to other modulation schemes such as
those used for coherent optical communication systems. For
instance, BPSK, PM-BPSK, QPSK, PM-QPSK, M-QAM, and PM-M-QAM
modulation schemes may each require coherent optical detection, and
pluggable photonics module 10 and host board 28 may be considered
as being part of a coherent optical communication system.
[0185] Coherent optical communication systems refer to optical
systems that utilize both magnitude and phase information for
transmitting and receiving data such as for phase-shift keying
modulation (e.g., BPSK, PM-BPSK, QPSK, PM-QPSK, M-QAM, or PM-M-QAM
modulation).
[0186] For example, in coherent optical communication systems,
pluggable photonics module 10 may rely on a beating between a
received signal and a local reference which maps both magnitude and
phase information of the received optical electric field in the
optical signal to measurable voltage or current. For instance,
coherent optical communication systems may use a local carrier
phase reference generated at pluggable photonics module 10 for the
reception of optical signals from network 32. For example, as
illustrated in more detail with respect to FIGS. 11 and 12,
photonics 12 of pluggable photonics module 10 relies on an external
laser source 34 and phase shifting optical hardware to mix pairs of
data streams received from host board 28 for transmission as a
single optical signal. Photonics 12 may also include the optical
hybrid mixers to convert the received optical signal into the pairs
(e.g., in-phase and quadrature phase) of data streams, referred to
as I and Q data streams, for transmission to host board 28.
[0187] In PSK modulation, binary ones and zeros are represented by
changing, or modulating, the phase of a carrier wave sometimes
referred to as a lightwave. In this manner, both the magnitude and
the phase of the optical signal are used to transmit data. For
example, both the magnitude and the phase information of the
received optical signal may be needed to recover the transmitted
data.
[0188] In some examples, in addition, the modulated lightwave in
one polarization may be multiplexed with another modulated
polarization, which may be orthogonal to the previous one, to
produce a polarization multiplexed (PM) signal, such as PM-QPSK.
The polarizations of the lightwave signals may be chosen to be
orthogonal to allow for a simple polarization beam splitter or
polarizer for polarization demultiplexing when photonics 12
receives data from network 32.
[0189] In this way. PM-QPSK may be considered as a combination of
two QPSK lightwave signals, where a first QPSK lightwave signal is
for a first polarization of the lightwave, and the second QPSK
lightwave signal is for a second polarization of the lightwave.
Each of the QPSK lightwave signals utilizes four phases to encode
two bits per symbol. Accordingly, PM-QPSK modulation utilizes four
phases to encode two bits per symbol per polarization, which
results in four bits per symbol.
[0190] For example, PM-QPSK modulation uses four input electrical
data streams per polarization to impart the complex information on
the optical carrier. The electrical signal for each polarization
contains a pair of in-phase (I) and quadrature (Q) data streams
that represent the complex data waveform. For example, in PM-QPSK
modulation, there may be two in-phase data streams and two
quadrature data streams, and one in-phase (I) data stream and one
quadrature (Q) data stream forms one pair of a complex number, and
the other I data stream and the other Q data stream forms another
pair of a complex number. Each of the in-phase and quadrature data
stream pairs may be nominally orthogonal to one another, in
polarization, once the electrical data streams impart their complex
information on the optical carrier. Each of these I or Q electrical
data streams can be single-ended or differential. For OOK
modulation, a single data stream is sufficient to impart the data
on the lightwave, and similarly, a single data stream is sufficient
to recover the data after detection by a photo-detector.
[0191] In PM-QPSK modulation, the input optical signal includes two
lightwaves that are polarized orthogonally with respect to one
another (e.g., one is horizontally polarized light, and the other
is vertically polarized light, as an illustrative example).
However, the polarization need not always be horizontal and
vertical polarized light, and need not always be orthogonal. For
ease of description, one of the lightwaves may be referred to as
lightwave with polarization 1, and the other as lightwave with
polarization 2. Each of the lightwaves may be associated with a
particular magnitude and phase. The magnitude and phase of each of
the lightwaves may be represented as a complex signal that includes
real and imaginary aspects.
[0192] For example, for PM-QPSK modulation, photonics 12 receives
an optical signal via optical link 30 that includes lightwave with
polarization 1 and lightwave with polarization 2. Optical
components within photonics 12 extract the lightwave with
polarization 1 and the lightwave with polarization 2 from the
received optical signal. The optical components further mix the
lightwave with polarization 1 with a lightwave output from a local
oscillator, received from external to the photonics 12 and received
from external to module 10, generate an in-phase optical data
stream, referred to as I.sub.1 to indicate that it is for the
lightwave with polarization 1, and to generate a quadrature optical
data stream, referred to as Q.sub.1 to indicate that it is for the
lightwave with polarization 1. The I.sub.1 data stream is
proportional to the real aspect of the complex signal of the
lightwave with polarization 1, and the Q.sub.1 data stream is
proportional to the imaginary aspect of the complex signal of the
lightwave with polarization 1.
[0193] Similarly, the optical components also mix the lightwave
with polarization 2 with a lightwave output from a local
oscillator, received from external to the photonics 12 and received
from external to module 10, to generate an in-phase optical data
stream, referred to as I.sub.2 to indicate that it is for the
lightwave with polarization 2, and to generate a quadrature optical
data stream, referred to as Q.sub.2 to indicate that it is for the
lightwave with polarization 2. Similar to I.sub.1 and Q.sub.1, the
I.sub.2 data stream is proportional to the real aspect of the
complex signal of the lightwave with polarization 2, and the
Q.sub.2 data stream is proportional to the imaginary aspect of the
complex signal of the lightwave with polarization 2.
[0194] In this manner, the pairs of I/Q optical data streams (e.g.,
a first pair that includes I.sub.1 and Q.sub.1, and a second pair
that includes I.sub.2 and Q.sub.2) together represent the received
optical signal. For example, I.sub.1 and Q.sub.1 together represent
the specific magnitude and phase of the lightwave with polarization
1, and I.sub.2 and Q.sub.2 together represent the specific
magnitude and phase of the lightwave with polarization 2. Also, in
this example, the lightwave with polarization 1 and the lightwave
with polarization 2 together form the original received optical
signal.
[0195] This relative increase in modulation complexity from a 10
Gbps data rate to a 100 Gbps data rate (e.g., from OOK modulation
to QPSK modulation) is part of scaling a WDM system from 10 Gbps to
100 Gbps. For example, additional care is taken to maintain signal
integrity because of the high data rate and the complex modulation.
For instance, because PM-QPSK modulation results in a plurality of
data streams (e.g., two pairs of I and Q data streams), with each
pair representing both magnitude and phase information of the
lightwave signal, the signal integrity for the pairs of data
streams is maintained to properly recover both the magnitude and
phase information of the received optical signal.
[0196] Such scaling may also increase cost. For example, the cost
for photonics needed for 10 Gbps may be substantially less than the
cost for photonics needed for 100 Gbps. Photonics, as used in this
disclosure, refers commonly to the hardware components such as
lasers and photodiodes needed for optical communication. For 100
Gbps with PM-QPSK modulation, the photonics include optical IQ
modulators for each of the polarization multiplexed data streams to
transmit data. To receive data, the photonics include optical
hybrid mixers for each polarization state. Photonics for 10 Gbps
with OOK modulation may not require such IQ modulators and optical
hybrid mixers, and may therefore be less costly.
[0197] In other techniques, because of the plurality of data
streams (e.g., four data streams for PM-QPSK modulation) and the
high data rates of the 100 Gbps systems, photonics and data
processing components such as analog-to-digital converters (ADCs)
and digital-to-analog converters (DACs) are on a common board. By
placing photonics and ADCs and DACs on a common board, there will
be minimal signal degradation between signals transmitted by the
photonics to the data processing components or received by the
photonics from the data processing components in 100 Gbps
systems.
[0198] In these other examples where the photonics for 100 Gbps
were not pluggable, because the components all resided on a common
board, the WDM system may incur prohibitive costs in upgrading from
a 10 Gbps WDM system to a 100 Gbps WDM system. For instance, one of
the major costs in upgrading to a 100 Gbps WDM system is the
photonics for 100 Gbps. It may be desirable to pre-populate the
slots within the WDM systems with boards, such as host board 28,
that operate at 100 Gbps, but defer costs associated with the
expensive photonics needed for 100 Gbps. However, boards for 100
Gbps WDM systems that include the photonics may not allow deferral
of costs associated with photonics and result in a relatively large
upfront cost for upgrading.
[0199] The photonics for a relatively higher data rate WDM system
(e.g., a 100 Gbps WDM system) can reside in a pluggable module,
such as pluggable photonics module 10, rather than on host board
28. In this manner, photonics functions such as mixing of optical I
and Q data stream pairs for PM-QPSK occur within pluggable
photonics module 10, and other functions such as ADC, DAC and
digital signal processing (DSP) functions occur on a different
board such as host board 28 or another board coupled to host board
28 that is further downstream, rather than both functions occurring
on a common board.
[0200] The pluggable design of pluggable photonics module 10 allows
deferral of photonics costs. For example, the 100 Gbps WDM system
may be pre-populated with a plurality of boards such as host board
28 for eventual upgrade to 100 Gbps. The cost of host board 28 may
be substantially less than the cost of the photonics needed for 100
Gbps. Then, when 100 Gbps data rates are needed, a plurality of
pluggable modules such as pluggable photonics module 10 are each
plugged into respective ones of host board 28. In this manner,
pluggable photonics module 10 provides a "pay as you grow" market
strategy by deferring costs associated with the 100 Gbps
photonics.
[0201] Also, pluggable photonics module 10 provides vendor options.
For example, one vendor may provide a better 100 Gbps version of
pluggable photonics module 10 compared to another vendor, and the
pluggable design of pluggable photonics module 10 allows selection
of the better 100 Gbps version of pluggable photonics module 10.
Moreover, it is unknown whether there will be further advances in
photonics technology, or whether the 100 Gbps WDM system will be
needed for special use cases. The pluggable design has flexibility
in upgrading to better versions of pluggable photonics module 10,
as well as flexibility in selecting the photonics module needed for
the special use cases.
[0202] As illustrated, host board 28 includes pluggable interface
21 and pluggable photonics module 10 includes pluggable interface
13, which is the reciprocal of pluggable interface 21. Pluggable
interface 13 and pluggable interface 21 mate with one another to
couple pluggable photonics module 10 to host board 28. With
pluggable interface 13 and pluggable interface 21, pluggable
photonics module 10 can be selectively coupled to or decoupled from
host board 28.
[0203] Pluggable interface 13 includes connection points 14A-14N
(collectively referred to as "connection points 14") and pluggable
interface 21 includes connection points 22A-22N (collectively
referred to as "connection points 22"). When pluggable photonics
module 10 couples to host board 28, connection points 14 mate with
corresponding connection points 22 to provide a continuous
electrical path for data transmission and reception between
pluggable photonics module 10 and host board 28.
[0204] For example, photonics 12 of pluggable photonics module 10
receives a downstream optical signal from network 32 via optical
link 30. In this example, the downstream optical signal is
modulated in accordance with the PM-QPSK modulation scheme.
Photonics 12 converts the downstream optical signal into two pairs
of I and Q optical data streams, and converts the two pairs of I
and Q optical data streams to two pairs of I and Q electrical data
streams (referred to as pairs of I/Q electrical data streams for
ease of reference). In this example, the pairs of I/Q electrical
data streams together represent magnitude and phase information for
the received optical signal. Photonics 12 transmits the pairs of
I/Q electrical data streams to host board 28 via the electrical
path provided by the mating of connection points 14 to connection
points 22.
[0205] Upstream, processor 24 transmits the pairs of I/Q electrical
data streams to photonics 12 via the electrical path provided by
the mating of connection points 22 to connection points 14.
Photonics 12 receives the pairs of I/Q electrical data streams, and
converts the pairs of I/Q electrical data streams into a single
optical signal for upstream transmission to network 32 via optical
link 30.
[0206] While pluggable photonics module 10 may provide cost
deferment and design flexibility, the pluggable design may degrade
the signal integrity of the pairs of I/Q electrical data streams
received or transmitted by host board 28. For example, the mating
of connection points 14 to connection points 22 may result in a
less than ideal connection between pluggable photonics module 10
and host board 28, referred to as physical impairments of mating
connection points 14 to connection points 22. For instance,
connection points 14 and connection points 22 may not line up
perfectly. Furthermore, even when connection points 14 and
connection points 22 line up as close to ideal as possible, the
connection between connection points 14 and connection points 22
may increase capacitance and inductance, as compared to if the
components of pluggable photonics module 10 were directly coupled
to the components of host board 28 (i.e., the components of
pluggable photonics module 10 resided on host board 28).
[0207] These physical impairments negatively impact the signal
integrity of the pairs of I/Q electrical data streams. For example,
the physical impairments distort the pairs of I/Q electrical data
streams transmitted by photonics 12. The increased capacitance and
inductance may distort the amplitude of the pairs of the I/Q
electrical data streams as a function of frequencies, as well as
the phase (e.g., group delay as a function of frequency).
[0208] Because the pairs of I/Q electrical data streams transmitted
by photonics 12 together represent the received optical signal,
such distortions added by the physical impairments may make it
difficult for processor 24 of host board 28 to accurately recover
the magnitude and phase information of the received optical signal,
and thereby increase the bit error rate (BER) to an undesirable
level. For instance, in this example, the electrical data streams
that processor 24 receives together represent the magnitude and
phase information of the received optical signal. However, these
electrical data streams also include electrical distortion caused
by pluggable interface 13 and pluggable interface 21, which make it
difficult for processor 24 to recover the magnitude and phase
information of the received optical signal.
[0209] Processor 24 may compensate for the electrical distortion
caused by pluggable interface 13 and pluggable interface 21 to
recover the magnitude and phase information of the received optical
signal. It should be understood that the recovered magnitude and
phase information of the received optical signal may not be
identical to the magnitude and phase information of the transmitted
optical signal. For example, the received optical signal may also
include optical distortion such as chromatic dispersion, as one
non-limiting example. In examples described in this disclosure,
processor 24 may also compensate for the optical distortion to
recover magnitude and phase information of the original,
transmitted optical signal.
[0210] For example, the optical signal that photonics 12 receives
includes optical distortion. The optical components within
photonics 12 extract the pairs of I and Q optical data streams.
These extracted pairs of I and Q optical data streams may not be
identical to the I and Q optical data streams that were mixed
together for transmission to photonics 12 because of the optical
distortion. After photonics 12 convert the pairs of I and Q optical
data streams into pairs of I and Q electrical data streams, the
pairs of I and Q electrical data streams represent the received
optical signal, which included optical distortion. Then, when
processor 24 receives the pairs of I and Q electrical data streams,
these pairs of I and Q electrical data streams include both
electrical distortion caused by pluggable interface 13 and
pluggable interface 21 and optical distortion that was part of the
received optical signal.
[0211] Processor 24 may compensate, on pairs of the I/Q electrical
data streams, for the electrical distortion caused by pluggable
interface 13 and pluggable interface 21 to recover the magnitude
and phase information of the received optical signal. Processor 24
may also compensate for the optical distortion to recover the
magnitude and phase information for the transmitted optical signal.
In this manner, the I/Q electrical data streams may be
substantially similar to the I/Q electrical data streams used to
generate the transmitted optical signal.
[0212] For example, processor 24 includes one or more complex
equalizers simultaneously compensating the amplitude (loss versus
frequency) and the phase (group delay versus frequency) distortion
due to physical impairments of the mating between pluggable
interface 13 and pluggable interface 21. The term complex
equalizers means that the equalizers operate on the real and
imaginary parts of the complex signal. For example, for PM-QPSK,
one equalizer may operate on the I.sub.1 and Q.sub.1 data streams
together because I.sub.1 represents the real aspect of the
lightwave with polarization 1 and Q.sub.1 represents the imaginary
aspect of the lightwave with polarization 1. Another equalizer may
operate on the I.sub.2 and Q.sub.2 data streams together because
I.sub.2 represents the real aspect of the lightwave with
polarization 2 and Q.sub.2 represents the imaginary aspect of the
lightwave with polarization 2. In another example, a single
equalizer may simultaneously compensate the amplitude and phase of
both pairs of I/Q data streams.
[0213] Examples of processor 24 include, but are not limited to, a
digital signal processor (DSP), a general purpose microprocessor,
an application specific integrated circuit (ASIC), a field
programmable logic array (FPGA), a combination thereof, or other
equivalent integrated or discrete logic circuitry. In some
examples, processor 24 may include other components for processing
purposes such as ADCs and DACs, as further described below.
Furthermore, although the one or more equalizers are described as
being internal to processor 24, aspects of this disclosure are not
so limited. These one or more equalizers may be external to
processor 24. Accordingly, host board 28 may be considered as
including the one or more equalizers.
[0214] The one or more equalizers receive distorted pairs of I/Q
electrical data streams from pluggable photonics module 10 and
modify the distorted pairs of I/Q electrical data streams to
compensate for the distortion caused by the signal traveling across
connection points 14 and connection points 22. The resulting
modified pairs of I/Q electrical data streams may be substantially
similar to the pairs of/Q electrical data streams outputted by
photonics 12.
[0215] The one or more equalizers may provide adaptive
compensation, fixed compensation, or configurable compensation. For
instance, the one or more equalizers may filter the received pairs
of I/Q electrical data streams to compensate for the distortion.
The filter shape for the equalizer filters may be adaptive, fixed,
or configurable.
[0216] For adaptive impairment removal, the one or more equalizers
estimate the amount of distortion caused by the physical
impairment, and adapt the amount of compensation that is applied
based on the estimated distortion. For fixed impairment removal,
the one or more equalizers are preset with the amount of
compensation, and provide the preset amount of compensation
regardless of the amount of distortion.
[0217] In some examples, it may be possible to configure the amount
of compensation that the one or more equalizers apply (i.e.,
configure the filter shape). For example, as illustrated in FIG.
10, pluggable photonics module 10 includes interface 20 and host
board 28 includes interface 26. Interface 20 and interface 26
couple to one another when pluggable photonics module 10 couples to
host board 28. When coupled, interface 20 transmits information to
interface 26 regarding pluggable photonics module 10, which
interface 26 forwards to processor 24. Based on the received
information, processor 24 may configure the amount of compensation
that the one or more equalizers apply.
[0218] For example, processor 24 may include a processing unit that
receives the information from interface 20 via interface 26. The
processing unit may utilize the received information to determine
the amount of compensation that the one or more equalizers of
processor 24 are to apply. In alternate examples, the processing
unit may be external to processor 24. In these examples, the
processing unit determines the amount of compensation that the one
or more equalizers of processor 24 are to apply, and configures the
one or more equalizers of processor 24 to apply the determined
amount of compensation.
[0219] For instance, as illustrated, pluggable photonics module 10
includes memory 16 and processor 18. Examples of processor 18
include, but are not limited to, a DSP, a general purpose
microprocessor, an ASIC, an FPGA, or other equivalent integrated or
discrete logic circuitry. Examples of memory 16 include, but are
not limited to, a random access memory (RAM), a read only memory
(ROM), an electrically erasable programmable read-only memory
(EEPROM), or other magnetic storage devices, flash memory, or any
other medium that can be used to store information.
[0220] Memory 16 stores information about pluggable photonics
module 10, and in some examples, information regarding the manner
in which pluggable photonics module 10 will be used. The vendor of
pluggable photonics module 10 may store such information in memory
16. In some examples, the vendor may also include information about
the performance of pluggable photonics module 10, such as
information that indicates that pluggable photonics module 10
includes low performance, low cost components, or low performance,
low power components.
[0221] For example, memory 16 may store information regarding
characteristics of the optical components of photonics 12,
information regarding the type of modulation provided by photonics
12 (e.g., the type of QPSK or M-QAM modulation), information that
provides an estimate of the amount of distortion caused by
connection points 14 mating with connection points 22 (e.g.,
changes in magnitude and phase as a function of frequency), and any
other type of information such as part number or vendor name
pertinent to the functionality or behavior of pluggable photonics
module 10 when coupled to host board 28. In some examples,
processor 18 also transmits status information of pluggable
photonics module 10. For example, if the components of photonics 12
are not functioning properly, processor 18 may transmit status
information (e.g., an alarm) to processor 24 via interface 20 and
interface 26.
[0222] When pluggable photonics module 10 is coupled to host board
28, processor 18 may retrieve the information stored in memory 16
and transmit the information to interface 20. Interface 20 converts
the information received from processor 18 to a communication
protocol for which interface 20 and interface 26 is configured.
Processor 24 receives the information from interface 26 and
determines the amount of compensation that the one or more
equalizers should apply based at least on the received
information.
[0223] Processor 24 may then configure the one or more equalizers
to apply the determined amount of compensation. For example, based
on information that indicates the changes in magnitude and phase,
as a function of frequency, due to the pairs of I/Q electrical data
streams traveling across pluggable interface 13 and pluggable
interface 21 (e.g., across connection points 14 and connection
points 22), processor 24 may determine the target filter shape that
the one or more equalizers apply to compensate for the distortion.
As another example, there may be a plurality of equalizer types
from which processor 24 may select the equalizer that will
compensate for the distortion. In this example, processor 24 may
select the appropriate equalizer type based on the received
information from processor 16.
[0224] In some examples, it may be sufficient for unidirectional
communication from pluggable photonics module 10 to host board 28.
In other embodiments host board 28 may transmit information to
pluggable photonics module 10 for bi-directional communication. As
one example, processor 24 transmits a command to processor 18, via
interface 26 and interface 20, that defines the amplitude of the
pairs of I/Q electrical data streams outputted by photonics 12.
Processor 18, in turn, adjusts the amplitude of the pairs of I/Q
electrical data streams outputted by photonics 12. As another
example, processor 24 may determine that some tuning on the optical
components of photonics 12 may result in better bit-error-rate
(BER). In this example, processor 24 transmits a command to
processor 18, via interface 26 and interface 20, that instructs
processor 18 to tune the optical components of photonics 12, which
processor 18 then tunes. Host board 28 and pluggable photonics
module 10 communicate other examples of information with one
another.
[0225] Interface 20 and interface 26 communicate with another using
any standard or proprietary protocol, and the techniques of this
disclosure are not limited to any specific communication protocol.
In general, the communication between interface 20 and interface 26
need not necessarily require complex communication formats or high
data rate communication; although, this may be possible. As one
example, interface 20 and interface 26 may communicate with one
another using the management data input/output (MDIO) protocol. In
this example, interface 20 and interface 26 are MDIO interfaces.
For example, MDIO interface 20 couples to MDIO interface 26 with a
serial bus and each transmits or receives information via the
serial bus. MDIO communication is provided for illustration
purposes only.
[0226] Processor 24 includes one or more complex equalizers to
compensate for the electrical distortion on the pairs of I/Q
electrical data streams received from pluggable photonics module 10
to recover the magnitude and phase information of the received
optical signal. These one or more equalizers are referred to as
receiver (RX)-equalizers. In some examples, processor 24 may also
include transmitter (TX)-equalizers that compensate the pairs of
I/Q electrical data streams transmitted by processor 24.
[0227] For example, similar to the received pairs of I/Q electrical
data streams, the data streams transmitted by processor 24 may be
distorted due to the physical impairments of connection points 22
and connection points 14. To address this distortion, the one or
more TX-equalizers modify the data streams transmitted by processor
24 before the signals travel across pluggable interface 21. For
example, the one or more TX-equalizers modify the data streams to
pre-compensate for the distortion such that after the physical
impairments of connection points 22 and connection points 14
distort the pre-compensated data streams, the resulting data
streams are substantially similar to the data streams transmitted
by processor 24. Similar to the RX-equalizers, the TX-equalizers
may be adaptive, fixed, or configurable.
[0228] FIGS. 11 and 12 are block diagrams illustrating examples of
photonics within a pluggable photonics module in accordance with
one or more examples such as any of FIGS. 1-10. For example, FIG.
11 illustrates components of photonics 12 that receive I/Q
electrical data streams from processor 24, convert the I/Q
electrical data streams into a QPSK modulated optical signal or
PM-QPSK modulated optical signal, and transmit the optical signal
to network 32. FIG. 12 illustrates components of photonics 12 that
receive a QPSK or PM-QPSK optical signal from network 32, convert
the optical signal into I/Q electrical data streams, and transmit
the I/Q electrical data streams to processor 24. FIGS. 11 and 12
are illustrated separately for ease of description. However,
photonics 12 includes both the transmit photonics illustrated in
FIG. 11 and the receive photonics illustrated in FIG. 12.
[0229] The components of photonics 12 are illustrated for PM-QPSK
modulation. Photonics 12 may include additional, fewer, or
different components than those illustrated based on the desired
PM-QPSK modulation. In alternate examples, photonics 12 includes
different components for different modulation schemes. For example,
if BPSK modulation is desirable, photonics 12 includes components
for coherent BPSK modulation. In general, photonics 12 includes
components needed for the desired type of coherent communication,
including even more complex modulation schemes such as multi-level
quadrature amplitude modulation (M-QAM where M>4).
[0230] As illustrated in FIG. 11, for the transmit photonics of
photonics 12 include polarization splitter (PS) 36, drive
amplifiers 37A-37D, modulators 38A and 38B, and polarization beam
combiner (PBC) 40. PBC 40 is coupled to optical link 30 and outputs
an optical modulated signal (e.g., a PM-QPSK modulated optical
signal). Also, as illustrated, photonics 12 receives I.sub.1',
Q.sub.1', I.sub.2', and Q.sub.2' data streams, which are electrical
data streams are outputted by processor 24 on host board 28 for
PM-QPSK modulation.
[0231] In this disclosure, the terms I.sub.1', Q.sub.1', I.sub.2',
and Q.sub.2' data streams are used to describe data streams that
processor 24 transmits to pluggable photonics module 10, and the
terms I.sub.1, Q.sub.1, I.sub.2, and Q.sub.2 data streams are used
to describe data streams that processor 24 receives from pluggable
photonics module 10. The I.sub.1', Q.sub.1', I.sub.2', and Q.sub.2'
data streams that processor 24 transmits may be different from the
I.sub.1, Q.sub.1, I.sub.2, and Q.sub.2 data streams that processor
24 receives. For example, the I.sub.1', Q.sub.1', I.sub.2', and
Q.sub.2' data streams are for downstream communication, while the
I.sub.1, Q.sub.1, I.sub.2, and Q.sub.2 data streams are for
upstream communication.
[0232] In FIG. 11, the I.sub.1' and Q.sub.1' data streams may form
a first pair of data streams that processor 24 transmits, and may
be for the lightwave with polarization 1. The I.sub.2' and Q.sub.2'
data streams may form a second pair of data streams that processor
24 transmits, and may be for the lightwave with polarization 2. In
some examples, the I.sub.1', Q.sub.1', I.sub.2', and Q.sub.2' data
streams data streams may be composed of differential data streams
that are AC coupled via capacitors to photonics 12.
[0233] In FIG. 11, the components of photonics 12 receive the
I.sub.1', Q.sub.1', I.sub.2', and Q.sub.2' data streams from
connection points 14, which mates with connection points 22 of host
board 28. In some examples, photonics 12 may include drive
amplifiers 37A-37D coupled to each one of the I.sub.1', Q.sub.1',
I.sub.2', and Q.sub.2' data streams. Drive amplifiers 37A-37D may
amplify the voltage level of the I.sub.1', Q.sub.1', I.sub.2', and
Q.sub.2' data streams outputted by host board 28.
[0234] Laser 34, received from external to the photonics 12 and
received from external to module 10, may be any type of laser that
is usable for high bit rate optical signal transmission, typically
a low linewidth laser in the 1550 nm wavelength range (so-called
C-Band), but can be any wavelength. Optical amplifiers operating in
same wavelength range may allow photonics 12 to transmit the
generated optical signal a relatively far distance. An example is
Erbium-Doped Fiber Amplifiers (EDFAs), which amplify light in the
1550 nm spectral region. The ability of photonics 12 to transmit
the generated optical signal a relatively far distance reduces the
number of intermittent optical-to-electrical-to-optical (O-E-O)
repeaters needed to regenerate the transmitted optical signal.
[0235] Polarization splitter (PS) 36 receives the light from laser
34 and splits the light into (at least) two paths. Each one of
modulators 38A and 38B receives light from one of the paths.
Modulators 38A and 38B modulate the light on the respective paths
with respective I/Q electrical data stream pairs. Modulators 38A
and 38B may be referred to as IQ modulators or Cartesian
modulators. In the example of 10, modulator 38A receives the
I.sub.1' and Q.sub.1' electrical data streams and modulates the
light to form a complex modulated lightwave signal, modulated in
both magnitude and phase, forming a QPSK signal. Modulator 38B
receives 12' and Q.sub.2' electrical data streams and modulates the
light to form a complex modulated lightwave signal, modulated in
both magnitude and phase, forming a second QPSK signal.
[0236] Polarization beam combiner (PBC) 40 receives the polarized
and modulated optical signals from each one of modulator 38A and
38B. For instance, the optical QPSK signals from modulators 38A or
38B are then multiplexed in (nominally orthogonal) polarization
using PBC 40. For example, PBC 40 combines the received QPSK
optical signals into nominally orthogonal polarizations into a
single polarization multiplexed (PM) optical signal and transmits
the PM-QPSK optical signal to network 32 via optical link 30. In
this manner, photonics 12 utilizes lightwave communications
techniques to generate and transmit an optical PM-QPSK signal.
[0237] As illustrated in FIG. 12, the receive photonics of
photonics 12 include polarization beam splitter (PBS) 42, local
oscillator (LO) 44 received from external to the photonics 12 and
received from external to module 10, polarization splitter (PS) 46,
optical hybrid mixers 48A and 48B, and photo-detectors (PDs)
50A-50D. PDs 50A-50D convert the magnitude of the optical signal to
an electrical representation. PBS 42 receives an optical signal
from network 32 via optical link 30 and splits the received optical
signal into first and second optical signals with nominally
orthogonal polarization (e.g., substantially orthogonal
polarization). Each one of optical hybrid mixers 48A and 48B
receive respective optical signals from the first and second
nominally orthogonal optical signals from PBS 42.
[0238] The receive photonics also include local oscillator 44
received from external to the photonics 12 and received from
external to module 10, which is a laser. Local oscillator 44
provides the phase reference required in coherent system to recover
the PM-QPSK optical waveform that photonics 12 receives. In some
examples, local oscillator 44 may be a free running oscillator. For
example, the laser signal outputted by local oscillator 44 may not
need to be phase-locked with the optical signal that PBS 42
receives.
[0239] Polarization splitter (PS) 46 receives the light from local
oscillator 44 from external to the photonics 12 and external to
module 10, and splits the light into (at least) first and second
light paths. PS 46 is substantially similar to PS 36 (FIG. 2A).
Each one of optical hybrid mixers 48A and 48B receive respective
local oscillator light from the first and second light paths from
the PS 46. In some examples, the location of PBS 42 and PS 46 may
be swapped with no loss of functionality, provided the light from
local oscillator 44 is split into two nominally orthogonally
polarized lightwaves.
[0240] Optical hybrid mixers 48A and 48B each mix the respective
optical signals from PBS 42 with the respective local oscillator
lightwave reference from PS 46 and output optical data stream
representing in-phase (I) and quadrature-phase (Q) components of
the PM-QPSK modulated signal. For example, optical hybrid mixer 48A
outputs I.sub.1 and Q.sub.1 optical data streams. Optical hybrid
mixer 48B outputs I.sub.2 and Q.sub.2 optical data streams. In some
examples, optical hybrid mixers 48A and 48B may be 90 degree
optical hybrid mixers. Also, in some examples, each one of the
I.sub.1, Q.sub.1, I.sub.2, and Q.sub.2 optical data streams may be
differentially encoded data streams.
[0241] Photo-detectors 50A-50D receive respective optical signals
of the I.sub.1, Q.sub.1, I.sub.2, and Q.sub.2 optical data streams
and convert these optical signals into electrical signals (e.g.,
the I.sub.1, Q.sub.1, I.sub.2, and Q.sub.2 data streams that
processor 24 receives). Photo-detectors 50A-50D may be composed of
a single photo-diode or a pair of nominally balanced photo-diodes.
A transimpedence amplifier (TIA) element for each photo-detector
may convert photo-current from the photo-diode(s) to a voltage
representation. However, the inclusion of TIA elements may not be
necessary in every example. The electrical output of each
photo-detector in 50A-50D can be single-ended or differential
electrical signals. In some examples, the TIA elements may include
automatic gain control (AGC) amplifiers, or the AGC amplifiers may
be external to the TIA elements. The AGC amplifiers may nominally
maintain output electrical voltage amplitude/swing for varying
input electrical current amplitude/swings.
[0242] In this manner, the receive photonics of photonics 12
convert the PM-QPSK modulated optical signal into electrical I and
Q data stream pairs (e.g., the I.sub.1, Q.sub.1, I.sub.2, and
Q.sub.2 data streams) representing the optical PM-QPSK signal for
further processing by processor 24 of host board 28. For example,
processor 24 receives the I.sub.1, Q.sub.1, I.sub.2, and Q.sub.2
electrical data stream pairs from photo-detectors 50A-50D through
the mating between connection points 14 and connection points
22.
[0243] The above detailed description includes references to the
accompanying drawings, which form a part of the detailed
description. The drawings show, by way of illustration, specific
embodiments in which the invention can be practiced. These
embodiments are also referred to herein as "examples." Such
examples can include elements in addition to those shown or
described. However, the present inventors also contemplate examples
in which only those elements shown or described are provided.
Moreover, the present inventors also contemplate examples using any
combination or permutation of those elements shown or described (or
one or more aspects thereof), either with respect to a particular
example (or one or more aspects thereof), or with respect to other
examples (or one or more aspects thereof) shown or described
herein.
[0244] In the event of inconsistent usages between this document
and any documents so incorporated by reference, the usage in this
document controls.
[0245] In this document, the terms "a" or "an" are used, as is
common in patent documents, to include one or more than one,
independent of any other instances or usages of "at least one" or
"one or more." In this document, the term "or" is used to refer to
a nonexclusive or, such that "A or B" includes "A but not B," "B
but not A," and "A and B," unless otherwise indicated. In this
document, the terms "including" and "in which" are used as the
plain-English equivalents of the respective terms "comprising" and
"wherein." Also, in the following claims, the terms "including" and
"comprising" are open-ended, that is, a system, device, article,
composition, formulation, or process that includes elements in
addition to those listed after such a term in a claim are still
deemed to fall within the scope of that claim. Moreover, in the
following claims, the terms "first," "second," and "third," etc.
are used merely as labels, and are not intended to impose numerical
requirements on their objects.
[0246] Geometric terms, such as "parallel", "perpendicular",
"round", or "square", are not intended to require absolute
mathematical precision, unless the context indicates otherwise.
Instead, such geometric terms allow for variations due to
manufacturing or equivalent functions. For example, if an element
is described as "round" or "generally round," a component that is
not precisely circular (e.g., one that is slightly oblong or is a
many-sided polygon) is still encompassed by this description.
[0247] The term "circuit" can include a dedicated hardware circuit,
a general-purpose microprocessor, digital signal processor, or
other processor circuit, and may be structurally configured from a
general purpose circuit to a specialized circuit such as using
firmware or software.
[0248] Any one or more of the techniques (e.g., methodologies)
discussed herein may be performed on a machine. In various
embodiments, the machine may operate as a standalone device or may
be connected (e.g., networked) to other machines. In a networked
deployment, the machine may operate in the capacity of a server
machine, a client machine, or both in server-client network
environments. In an example, the machine may act as a peer machine
in peer-to-peer (P2P) (or other distributed) network environment.
The machine may be a personal computer (PC), a tablet PC, a set-top
box (STB), a personal digital assistant (PDA), a mobile telephone,
a web appliance, a network router, switch or bridge, or any machine
capable of executing instructions (sequential or otherwise) that
specify actions to be taken by that machine. Further, while only a
single machine is illustrated, the term "machine" shall also be
taken to include any collection of machines that individually or
jointly execute a set (or multiple sets) of instructions to perform
any one or more of the methodologies discussed herein, such as
cloud computing, software as a service (SaaS), other computer
cluster configurations.
[0249] Examples, as described herein, may include, or may operate
by, logic or a number of components, or mechanisms. Circuit sets
are a collection of circuits implemented in tangible entities that
include hardware (e.g., simple circuits, gates, logic, etc.).
Circuit set membership may be flexible over time and underlying
hardware variability. Circuit sets include members that may, alone
or in combination, perform specified operations when operating. In
an example, hardware of the circuit set may be immutably designed
to carry out a specific operation (e.g., hardwired). In an example,
the hardware of the circuit set may include variably connected
physical components (e.g., execution units, transistors, simple
circuits, etc.) including a computer readable medium physically
modified (e.g., magnetically, electrically, moveable placement of
invariant massed particles, etc.) to encode instructions of the
specific operation. In connecting the physical components, the
underlying electrical properties of a hardware constituent are
changed, for example, from an insulator to a conductor or vice
versa. The instructions can enable embedded hardware (e.g., the
execution units or a loading mechanism) to create members of the
circuit set in hardware via the variable connections to carry out
portions of the specific operation when in operation. Accordingly,
the computer readable medium is communicatively coupled to the
other components of the circuit set member when the device is
operating. In an example, any of the physical components may be
used in more than one member of more than one circuit set. For
example, under operation, execution units may be used in a first
circuit of a first circuit set at one point in time and reused by a
second circuit in the first circuit set, or by a third circuit in a
second circuit set at a different time.
[0250] Particular implementations of the systems and methods
described herein may involve use of a machine (e.g., computer
system) that may include a hardware processor (e.g., a central
processing unit (CPU), a graphics processing unit (GPU), a hardware
processor core, or any combination thereof), a main memory and a
static memory, some or all of which may communicate with each other
via an interlink (e.g., bus). The machine may further include a
display unit, an alphanumeric input device (e.g., a keyboard), and
a user interface (UI) navigation device (e.g., a mouse). In an
example, the display unit, input device and UI navigation device
may be a touch screen display. The machine may additionally include
a storage device (e.g., drive unit), a signal generation device
(e.g., a speaker), a network interface device, and one or more
sensors, such as a global positioning system (GPS) sensor, compass,
accelerometer, or other sensor. The machine may include an output
controller, such as a serial (e.g., universal serial bus (USB),
parallel, or other wired or wireless (e.g., infrared (IR), near
field communication (NFC), etc.) connection to communicate or
control one or more peripheral devices (e.g., a printer, card
reader, etc.).
[0251] The storage device may include a machine readable medium on
which is stored one or more sets of data structures or instructions
(e.g., software) embodying or utilized by any one or more of the
techniques or functions described herein. The instructions may also
reside, completely or at least partially, within the main memory,
within static memory, or within the hardware processor during
execution thereof by the machine. In an example, one or any
combination of the hardware processor, the main memory, the static
memory, or the storage device may constitute machine readable
media.
[0252] While the machine readable medium can include a single
medium, the term "machine readable medium" may include a single
medium or multiple media (e.g., a centralized or distributed
database, and/or associated caches and servers) configured to store
the one or more instructions.
[0253] The term "machine readable medium" may include any medium
that is capable of storing, encoding, or carrying instructions for
execution by the machine and that cause the machine to perform any
one or more of the techniques of the present disclosure, or that is
capable of storing, encoding or carrying data structures used by or
associated with such instructions. Non-limiting machine readable
medium examples may include solid-state memories, and optical and
magnetic media. In an example, a massed machine readable medium
comprises a machine readable medium with a plurality of particles
having invariant (e.g., rest) mass. Accordingly, massed
machine-readable media are not transitory propagating signals.
Specific examples of massed machine readable media may include:
non-volatile memory, such as semiconductor memory devices (e.g.,
Electrically Programmable Read-Only Memory (EPROM), Electrically
Erasable Programmable Read-Only Memory (EEPROM)) and flash memory
devices; magnetic disks, such as internal hard disks and removable
disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.
[0254] The instructions may further be transmitted or received over
a communications network using a transmission medium via the
network interface device utilizing any one of a number of transfer
protocols (e.g., frame relay, internet protocol (IP), transmission
control protocol (TCP), user datagram protocol (UDP), hypertext
transfer protocol (HTTP), etc.). Example communication networks may
include a local area network (LAN), a wide area network (WAN), a
packet data network (e.g., the Internet), mobile telephone networks
(e.g., cellular networks), Plain Old Telephone (POTS) networks, and
wireless data networks (e.g., Institute of Electrical and
Electronics Engineers (IEEE) 802.11 family of standards known as
Wi-Fi.RTM., IEEE 802.16 family of standards known as WiMax.RTM.),
IEEE 802.15.4 family of standards, peer-to-peer (P2P) networks,
among others. In an example, the network interface device may
include one or more physical jacks (e.g., Ethernet, coaxial, or
phone jacks) or one or more antennas to connect to the
communications network. In an example, the network interface device
may include a plurality of antennas to wirelessly communicate using
at least one of single-input multiple-output (SIMO), multiple-input
multiple-output (MIMO), or multiple-input single-output (MISO)
techniques. The term "transmission medium" shall be taken to
include any intangible medium that is capable of storing, encoding
or carrying instructions for execution by the machine, and includes
digital or analog communications signals or other intangible medium
to facilitate communication of such software.
[0255] Method examples described herein can be machine or
computer-implemented at least in part. Some examples can include a
computer-readable medium or machine-readable medium encoded with
instructions operable to configure an electronic device to perform
methods as described in the above examples. An implementation of
such methods can include code, such as microcode, assembly language
code, a higher-level language code, or the like. Such code can
include computer readable instructions for performing various
methods. The code may form portions of computer program products.
Further, in an example, the code can be tangibly stored on one or
more volatile, non-transitory, or non-volatile tangible
computer-readable media, such as during execution or at other
times. Examples of these tangible computer-readable media can
include, but are not limited to, hard disks, removable magnetic
disks, removable optical disks (e.g., compact disks and digital
video disks), magnetic cassettes, memory cards or sticks, random
access memories (RAMs), read only memories (ROMs), and the
like.
[0256] The above description is intended to be illustrative, and
not restrictive. For example, the above-described examples (or one
or more aspects thereof) may be used in combination with each
other. Other embodiments can be used, such as by one of ordinary
skill in the art upon reviewing the above description. The Abstract
is provided to comply with 37 C.F.R .sctn. 1.72(b), to allow the
reader to quickly ascertain the nature of the technical disclosure.
It is submitted with the understanding that it will not be used to
interpret or limit the scope or meaning of the claims. Also, in the
above Detailed Description, various features may be grouped
together to streamline the disclosure. This should not be
interpreted as intending that an unclaimed disclosed feature is
essential to any claim. Rather, inventive subject matter may lie in
less than all features of a particular disclosed embodiment. Thus,
the following claims are hereby incorporated into the Detailed
Description as examples or embodiments, with each claim standing on
its own as a separate embodiment, and it is contemplated that such
embodiments can be combined with each other in various combinations
or permutations. The scope of the invention should be determined
with reference to the appended claims, along with the full scope of
equivalents to which such claims are entitled.
* * * * *